This invention relates generally to radomes, and, in particular to radomes attached to supersonic aircraft. Of particular concern is the ability of these radomes to have a greater field life in hostile rain impact environments.
As rain impacts on a radome moving at high speeds, the radome can be degraded within a short time. The construction of the radome involves a balance between the electrical properties of the radome and its aerodynamic qualities. This is particularly so when the radome must be able to withstand rain impact at Mach 1 and have the ability to operate with broadband antennae.
A conventional radome made of epoxy impregnated quartz laminated upon epoxy reenforced honeycomb material, for example, has limitations under the environmental conditions noted above. A conventional c-sandwich radome wall made of the materials noted above has been tested on a rotating arm under a controlled rainfall. At a speed of 500 miles per hour, a wall section lasted only 4 minutes with the rain incident at 90.degree. degrees, only 20 minutes with the rain incident at 60 degrees and no damage after 60 minutes with the rain incident at 30 degrees.
A primary handicap contributing to limited rain impact performance is the radome shape needed to satisfy the electrical objective of the contained broadband antenna. Increasing the fineness ratio, length of radome to base diameter, reduces the aerodynamic and rain impact loads; however, streamlining the radome beyond approximately 0.7 causes a negative effect on antenna electrical performance. Another drawback working against rain impact resistance is the inherent brittleness or low impact strength of epoxy resins and of the substrate bond interfaces which encourage the opportunity for delimination. The honeycomb core also obtains its strength by successive dippings into epoxy.
After the core buckels once, causing the epoxy to crack, the compressive strength essentially becomes zero and "soft spots" develop. Any attempt to increase the substrate layer thickness or honeycomb density would decrease the required electrical performance. Realizing the radome shape and material limitations, the task then centers around selecting alternate materials that demonstrate a significant increase in rain impact resistance without sacrificing electrical performance. The primary property used to select an alternate material to maintain similar electrical performance is the dielectric strength.
There currently exists, therefore, a need for a supersonic radome that optimizes electrical properties and aerodynamic qualities under a rainy environment. The present invention is directed toward satisfying that need.